node_promise_simple_sample.js

// Simple sample for explaining the resolve and reject of Promise

async function test(flag) {
    //
    return new Promise((resolve, reject)=>{
        if(flag) {
            resolve(0)
        } else {
            reject(-1)
        }
    })
}


async function main() {

    // 1. use then/catch
    test(true).then((rc)=>{
        console.log('1.resolve', rc)
    }).catch((err)=>{
        console.log('1.reject', err)
    })

    test(false).then((rc)=>{
        console.log('1.resolve', rc)
    }).catch((err)=>{
        console.log('1.reject', err)
    })

    // 2. use await/catch
    let rc
    try{ 
        rc = await test(true) // resolve
        console.log('2.resolve', rc)
    } catch(err) {
        console.log('2.reject', err)
    }

    try{ 
        rc = await test(false) // reject
        console.log('2.resolve', rc)
    } catch(err) {
        console.log('2.reject', err)
    }


}

main()